5.9.2.2 An Older Approach to Properties

Traditionally, Lisp systems provide a different object property
interface to that provided by make-object-property, in which the
object property that is being set or retrieved is indicated by a symbol.

Guile includes this older kind of interface as well, but it may well be
removed in a future release, as it is less powerful than
make-object-property and so increases the size of the Guile
library for no benefit. (And it is trivial to write a compatibility
layer in Scheme.)